HTTPS-crippling attack threatens tens of thousands of Web and mail servers

Tens of thousands of HTTPS-protected websites, mail servers, and other widely used Internet services are vulnerable to a new attack that lets eavesdroppers read and modify data passing through encrypted connections, a team of computer scientists has found.

The vulnerability affects an estimated 8.4 percent of the top one million websites and a slightly bigger percentage of mail servers populating the IPv4 address space, the researchers said. The threat stems from a flaw in the transport layer security protocol that websites and mail servers use to establish encrypted connections with end-users. The new attack, which its creators have dubbed Logjam, can be exploited against a subset of servers that support the widely used Diffie-Hellman key exchange, which allows two parties that have never met before to negotiate a secret key even though they're communicating over an unsecured, public channel.